1. Field of the Invention
The present invention relates to a preform wire used in manufacturing a carbon fiber reinforced aluminum composite material and a method for manufacturing the same.
2. Description of the Prior Art
Carbon fiber reinforced metal composite materials (hereinafter referred to as carbom/metal composites), which consist essentially of metal, as a matrix, and carbon fibers, as reinforcements, are higher in specific strength and specific modulus than monolithic metal. Therefore, the carbon/metal composites are regarded as promising materials in various fields of industry. Among these materials, the carbon/metal composites whose matrix is formed of aluminum or aluminum alloy, that is, carbon fiber reinforced aluminum composite material (hereinafter referred to as C/Al), is especially high in specific strength and specific modulus. Accordingly, the C/Al is considered a highly promising lightweight structural material for use in various industrial fields, such as in the aerospace industries.
In general, carbon fibers are poor in wettability with molten aluminum or aluminum alloy, while they tend to react easily with aluminum at high temperature, thereby deteriorating their properties. Accordingly, various measures have been taken to improve the wettability and prevent the reaction with aluminum.
In Japanese Patent Publication No. 59-12733, for example, there is a statement that the wettability of carbon fibers can be effectively improved by coating them with titanium boride or a mixture of titanium carbide and titanium boride. According to this method, however, the reaction between the carbon fibers and aluminum cannot be fully prevented. Furthermore, when "Thornel" 300 (manufactured by Union Carbide Co., Ltd., U.S.A.), which is of the so-called high-strength type, is used for the carbon fibers, and when AA202 is used as the aluminum alloy, the tensile strength of the C/Al is only 0.24 GPa when the carbon-fiber content (hereinafter referred to as V.sub.f) in the C/Al is 29% (see "Journal of Composite Materials" vol. 10, pp. 279 to 296, October, 1976), due to a reaction given by EQU 4Al+3C.fwdarw.Al.sub.4 C.sub.3.
In Japanese Patent Disclosure No. 61-69448, on the other hand, there is a statement that if carbon fibers are coated with carbon and then further coated with a material mainly composed of metal carbide or the like, a reaction between the carbo fiber and the aluminum is prevented, and a preform wire with a tensile strength equivalent to 86% of an estimated strength based on the rule of mixture can be obtained. However, the wettability can hardly be improved by the coating of these materials, and it is necessary that the carbon fibers are further coated with a material consisting essentially of titanium or boron. This results in a substantial increase in manufacturing cost, and requires more complicated processes.
Japanese Patent Laid-Open No. 61-130439 discloses a preform wire having a V.sub.f of 50% and a tensile strength of 1.5 GPa, which is composed of a continuous bundle of untreated carbon fibers and is infiltrated with aluminum. These untreated fiber bundles, whose surface is not treated for oxidation, are not highly reactive to aluminum, and have an elastic modulus of 373 GPa or more, in the direction of the fiber axis. Since these untreated carbon fibers with high modulus are less active or have smaller surface energy than those carbon fibers (hereinafter referred to as surface-treated carbon fibers) whose surface is treated for oxidation, the former have an advantage over the latter in being less susceptible to a deteriorative reaction. On the other hand, a material to improve wettability between carbon and aluminum cannot easily adhere to the untreated carbon fibers, so that preform wires obtained with use of these untreated carbon fibers cannot enjoy high productivity.